The present invention relates to an information recording medium for recording information therein when receiving an energy beam and also to an information recording and reproducing apparatus which uses the information recording medium. More particularly, the present invention concerns an erasable optical disk such as a phase change type optical disk or a magneto-optical disk and also concerns an information recording and reproducing apparatus capable of reproducing information from the erasable optical disk and a read-only optical disk.
This type of technique is disclosed in JP-A-272032 in which two metallic layers are provided so that first one of the two first and second metallic layers closer to a recording layer is set to be lower in thermal conductivity than the other second metallic layer, the first metallic layer is disposed as opposed to the second metallic layer, and the recording layer is disposed between the first and second metallic layers.
Further disclosed in a Proceeding of International Symposium on Optical Memory, 1995, pp. 151 and 152 is the fact that a semiconductor thin film of Si or the like material having a large transmittance is used in place of the aforementioned first metallic layer.
In general, reproduction compatibility conditions of the information recording and reproducing apparatus with the read-only optical disk are that the stabilities of tracking servo, focusing servo, etc. should be taken into consideration, a medium reflectivity be 15% or more, and the modulation of a reproduced signal be 50% or more when the quality of the reproduced signal is taken into consideration.
Known as one of information recording media satisfying the above conditions is such an information recording medium using a metal such as Au having a high reflectivity as shown in a paper entitled xe2x80x9cA CD-compatible erasable discxe2x80x9d, by J. H. Coombs, et al., in Proceedings of Topical Meeting on Optical Data Storage, 1994, pp. 94-106. Also known as another information recording medium is an information recording and reproducing system for recording, on such an information recording medium, information modulated based on the same modulation system as the read-only optical disk or an information reproducing system therefor. An optical recording disk is disclosed in JP-A-6-76361.
It is therefore an object of the present invention to provide an information recording medium which can provide a good recording sensitivity and produce a good reproduced signal, and also to provide an information recording and reproducing apparatus using the above information recording medium, which can have a high reliability at the time of recording and reproducing information.
In accordance with a first aspect of the present invention, there is provided an information recording medium which comprises a recording layer for recording information in the form of a recording mark based on atomic array change and/or electronic state change caused by irradiation of an energy beam, the recording mark being reproduced by irradiating the energy beam on the recording mark; and first and second metallic layers formed as opposed to an energy beam incident side of the recording layer and having different compositions, and wherein first one of the first and second metallic layers disposed closer to the recording layer contains Al, Cu, Ag, Au, Pt and Pd as its main components and a sum of contents of these atoms is 60% or more.
In the present invention, the second metallic layer contains Al, Cu, Ag, Au, Pt and Pd as its main components and a sum of contents of these atoms is larger than that of the first metallic layer.
In accordance with a second aspect of the present invention, there is provided an information recording and reproducing apparatus for reproducing information from an information recording medium, which apparatus comprises the information recording medium of the aforementioned first aspect including a recording layer for recording information in the form of a recording mark based on atomic array change and/or electronic state change caused by irradiation of an energy beam, the recording mark being reproduced by irradiating the energy beam on the recording mark, and also including first and second metallic layers formed as opposed to an energy beam incident side of the recording layer and having different compositions, wherein first one of the first and second metallic layers disposed closer to the recording layer contains Al, Cu, Ag, Au, Pt and Pd as its main components and a sum of contents of these atoms is 60% or more; a laser beam irradiating circuit for reproducing the recording mark from the information recording medium; and an address information detecting circuit for detecting address information from an electrical signal obtained by reproducing an address information mark provided on the information recording medium.
In accordance with a third aspect of the present invention, there is provided an information recording and reproducing apparatus for recording and reproducing information in and from an information recording medium, which apparatus comprises the information recording medium of the aforementioned first aspect including a recording layer for recording information in the form of a recording mark based on atomic array change and/or electronic state change caused by irradiation of an energy beam, the recording mark being reproduced by irradiating the energy beam on the recording mark, and also including first and second metallic layers formed as opposed to an energy beam incident side of the recording layer and having different compositions, wherein first one of the first and second metallic layers disposed closer to the recording layer contains Al, Cu, Ag, Au, Pt and Pd as its main components and a sum of contents of these atoms is 60% or more; a laser beam irradiating circuit for recording and reproducing the recording mark on and from the information recording medium; and a recorded signal modulating circuit and a recorded signal demodulating circuit for performing the recording operation of the recording marks having lengths associated with an information signal.
In accordance with yet a fourth aspect of the present invention, there is provided an information recording and reproducing apparatus in which a protective layer of a recording medium is made up of 2 first and second layers. The first protective layers is made of (ZnS)80(SiO2)20 (molar ratio). However, the first protective layer may be made of preferably a mixture composition (15-20 mol % of SiO2) of ZnS and SiO2 having a mixture ratio different from the above case or a mixture composition of ZnS and 10-40 mol % of oxide which will be given below, though its recording sensitivity and jitter become somewhat bad when compared with the above case. The oxide to be mixed in the above case is preferably SiO2, SiO, TiO2, Al2O3, Y2O3, CeO, La2O3, In2O3, GeO, GeO2, PbO, SnO, SnO2, Bi2O3, TeO2, WO2, WO3, SC2O3, Ta2O5 or ZrO2. Usable as the material of the protective layer in addition to the above is an oxide such as Sixe2x80x94Oxe2x80x94N material or Sixe2x80x94Alxe2x80x94Oxe2x80x94N material, or Crxe2x80x94O material such as Cr2O3, CrO or Coxe2x80x94O material such as Co2O3, CoO, an nitride such as TaN, AlN, Sixe2x80x94N material such as Si3N4, Alxe2x80x94Sixe2x80x94N material (e.g., AlSiN2), or Gexe2x80x94N material a sulfide such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS or Bi2S3, a selenide such as SnSe2, Sb2Se3, CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe or Bi2Se3, a fluoride such as CeF3, MgF2 or CaF2, a composition close to the above material, or a mixture of the above materials. It is highly profitable that the protective layer comprise multi-layers of the protective layers of the ZnS-based material and a third protective layer of material other than the above ZnS-based material. In this case, the material other than the above ZnS-based material is preferably any one of an oxide, a nitride or a fluoride.
In addition to the above material, the Al2O3 of the third protective layer may be replaced more preferably by such material containing Al2O3 as its main component or SiO2 as its main component, because an jitter increase appearing in the vicinity of a trailing-edge at number of rewriting of 10-100 times can be made low.
The material of the third protective layer is higher in thermal conductivity than (ZnS)80(SiO2)20. Thus, the thickness of the third protective layer is preferably in a range of not smaller than 2 nm and not larger than 20 nm and more preferably in a range of not smaller than 4 nm and not larger than 8 nm. Such a 2-film protective layer can act to prevent the adverse influences caused by the diffusion of the material of the first protective layer into the recording layer, even when the first metallic layer of the present invention is absent or made of Si, or even when another layer is added as when such a metallic layer that is as thin as that 50% or more of read light can transmit therethrough is added between the substrate and first protective layer. Further, when a fourth protective layer made of any of the materials usable as the material of the third protective layer is provided between the recording layer and second protective layer, more enhanced effects can be obtained. The thickness of the fourth protective layer may be set to be similar to as in the third protective layer.
With the above arrangement of the information recording medium in accordance with the present invention, as mentioned above, the reflectivity can be made to be 15% or more that is sufficient for the tracking servo and focusing servo, and the reproduced signal modulation also can be made to be 50% or more. Further, since the information recording medium has the plurality of metallic layers, the optical demand can be satisfied by the reflection of the first metallic layer while the thermal characteristics can be satisfied by the thermal conduction of the other metallic layer.
In particular, when the first metallic layer contains Al, Cu, Ag, Au, Pt and Pd as its main components and the sum of contents of these atoms is set to be not smaller than 70% and not larger than 85%; the thermal conductivity can be reduced to 1/10 or less, thus improving the recording sensitivity in the record mode.
Among these metals having high reflectivity, especially Al has a small wavelength dependency on the reflectivity and relatively inexpensive. Thus, Al is most excellent because it enables easy reduction of the thermal conductivity by a minute amount of addition of Al.
Further, when the second metallic layer having a composition different from that of the first metallic layer is provided on a side of the first metallic layer opposite to the light incident side, and the compositions of the first and second metallic layers are set so that the second metallic layer is higher in the thermal conductivity and strength than the first metallic layer; there is provided an information recording medium which can provide an enhanced inter-mark thermal interference suppressing effect in the record mode, can provide a good quality of reproduced signal and a high productivity.
Furthermore, the provision of the first metallic layer having the relatively low thermal conductivity enables the total thickness of the metallic layers to be made large without reduction of the recording sensitivity. As a result, the recording layer flow of the information recording medium can be highly effectively suppressed.
The provision of a third metallic layer having a reflectivity higher than that of the first metallic layer between the second and first metallic layers enables further improvement of the optical characteristics of the information recording medium such as the reflectivity and modulation.
When a non-metallic layer having a low thermal conductivity is provided between the first and second metallic layers, the thermal characteristics can be further improved, the recording sensitivity can be made high and the thermal interference between the recording marks can be suppressed.
In the present invention, in the case of the information recording medium of a land/groove recording type in which a transparent substrate is formed therein with grooves and recording marks are recorded for both of the lands and grooves, the medium can exhibit great effects. In the case where a track pitch is smaller than the diameter (corresponding to xcex/NA, where NA is the numerical aperture of an objective lens for condensing a laser beam of wavelength xcex used as the energy beam on the information recording medium) of the energy beam, there can be realized a high density recording without any generation of cross-erase.
In the information recording medium of the present invention, since the influence of the inter-mark thermal interference in the record mode is minimized, even when mark edge recording is carried out, the recording mark can be controlled to have a suitable length.
In addition, even when such a magnetic modulation recording system that a constant level of laser beam is irradiated on a disk and the orientation of an external magnetic field is modulated to record information, is employed as typically a magneto-optic disk; the information recording medium of the present invention is suitable for it. Even when the present invention is applied to a light intensity modulation system in which power level of the energy beam (laser beam) is modulated to record information, the invention can exhibit great effects. In the case of the light intensity modulation recording system, more in detail, heat tends to easily transmitted on the plane of the recording layer, which tends to influence the shape of the recording mark previously recorded or to be later recorded (thermal interference).
In the information recording medium of the present invention, on the other hand, heat is diffused selectively from the first metallic layer to the second metallic layer, thus minimizing the thermal diffusion onto the plane of the recording layer.
The above third protective layer acts to prevent mutual diffusion of the material of the first protective layer and the material of the recording layer and as a result to prevent change of the reflectivity which appears by a large number of overwriting operations. When the third layer has a thickness less than 2 nm, the effect was small. When the third layer has a thickness of not smaller than 2 nm, its reflectivity change can be suppressed to 3% or less and reached practical stability level or less. When the third layer is 4 nm thick, its reflectivity change was 2%. When the layer has a thickness of not smaller than 4 nm, its reflectivity change is not so largely different from the case of 4 nm.
Further, the phase change recording system generally tends to cause the flow of the recording layer or a change in the shape of the layer after many rewriting operations. The information recording medium of the present invention can easily suppress such deterioration.
Use of the recording layer of the composition suitable for the information recording medium of the invention enables video information compressed by such a video compression system as MPEG2 or data equivalent thereto to be recorded at an equivalent data transmission rate.
When the information recording medium of the present invention is used in the above information recording and reproducing apparatus, there is implemented an information recording and reproducing system which can record information with a high density, can output a good quality of reproduced signal and also can reproduce even a read-only optical disk.